I. Field of the Invention
This invention relates to milled teeth sealed bearing rock bits.
More particularly, this invention relates to milled teeth rotary cone rock bits, having tungsten carbide inserts dispersed in a heel row of each of the cones--the gage row milled teeth having partial hardfacing on the gage cutting side of each tooth.
II. Description of the Prior Art
Maintaining the gage diameter of an earthen borehole utilizing rotary cone rock bits is critical during operation of the rock bits in a borehole. If a rotary cone rock bit should become under gage or is worn to the point of cutting a hole diameter smaller than the original gage of the new bit, then subsequent full gage diameter rock bits will pinch and the rate of penetration will become less due to the under gage condition of the borehole.
Moreover, directional drilling has become more and more prevalent as the world oil resources become more scarce. Tapping into existing oil reserves or previously unattainable oil fields from a direction other than vertical is the most prevalent state-of-the-art method to most effectively utilize these resources. Rotary cone rock bits used in directional drilling are more subjected to bit side loads because the bit is forced to turn away from a straight or vertical penetration. Typically, a rotary cone is connected to a mud motor to drive the bit downhold. The gage rows of each of the rotary cones on the rock bit are more severely affected because of the side loads imparted to the bit during directional drilling operations.
State of the art milled teeth rotary cone rock bits utilized in drilling directional boreholes are less effective when the gage teeth wear. As the gage row teeth wear, the cutting of the gage or diameter of the borehole is compromised. In directional drilling operations, the gage row on each cone of the rotary cone rock bit must be sharp to allow the bit to change direction as it penetrates the formation. The increased area exposed by the worn gage row teeth gradually (as the bit wears) become bearing surfaces against the borehole peripheral sidewalls and it is increasingly more difficult to steer the bit in directional drilling operations.
The present invention addresses the method in which gage is cut in a borehole. Each of the milled teeth on the gage row of a milled tooth cone is partially hardfaced to extend beyond the core steel tooth on the cutting side of the tooth. The heel row adjacent to the gage row is relieved (recessed from the cone surface) and tungsten carbide or similar wear resistant inserts are equidistantly spaced in the recessed portion of the heel row. It would be obvious to space the inserts however randomly. The tungsten carbide teeth act to cut the gage of the borehole as the gage row milled teeth wear. This configuration is particularly effective in directional drilling where side loads on the drill bit particularly affect the ability to maintain gage of the borehole during directional drilling operations as heretofore described.
U.S. Pat. No. 3,134,447 teaches a tungsten carbide rotary cone rock bit having flush type tungsten carbide inserts imbedded in a heel row of each cone. The flush type inserts serve to prevent the heel portion of the bit from excessive wear, but dues not aid in cutting gage as the rock bit works in a borehole.
The present invention will tungsten carbide inserts projecting beyond the recessed heel surface of each cone aid in cutting gage as the rotary cones work in a borehole.
U.S. Pat. No. 2,774,571 illustrates a tungsten carbide rotary cone rock bit with extended tungsten carbide inserts in a gage of a rotary cone. The inserts in the gage are the primary gage cutting inserts and when they wear, the rotary cone bit will become under gage. The present invention describes milled teeth rotary cones with the gage row of milled teeth having extended hardened surfaces to cut gage with a backup series of equidistantly spaced tungsten carbide inserts that extend away from the heel row surface to further enhance or cooperate with the gage cutting milled teeth.
The prior art therefore is disadvantaged in that, when the gage cutters wear, whether the gage row is milled teeth or tungsten carbide inserts, the bit gage will go undersize leading to problems such as slow rate of penetration and for subsequent full gage rotary cone bits as heretofore described.
The present invention overcomes these disadvantages by providing enhanced gage cutting capabilities. This invention has particular application for drilling wherein the rotary cone rock bits are driven by a downhole mud motor during directional drilling operations.